In the field of a crystalline silicon solar cell, silicon substrates have been reduced in thickness in order to reduce the amount of silicon usage and to improve the conversion efficiency of silicon substrates. Unfortunately, thinner silicon substrates have remarkably lower conversion efficiency. The reason for this is, for example, that a large number of defects in the front surface of the silicon substrate having conductivity mainly cause the reduction in the lifetime of minority carriers (for example, electrons in a p-type substrate) generated by light irradiation. Thus, reducing the loss of minority carriers eventually improves the conversion efficiency of solar cells.
To regulate the reduction in the lifetime of carries, a passivation film is generally formed on the surface of a silicon substrate. An aluminum oxide film, one of a plurality of kinds of passivation films, has received attention because of its higher passivation effect (the function to regulate the reduction in lifetime) on the p-type silicon substrate.
The aluminum oxide films include negative fixed charges and are known to produce the passivation effect resulting from the field effect caused by the fixed charges. That is, when the passivation film made of the aluminum oxide film including negative fixed charges is formed on the front surface of the p-type silicon substrate the diffusion of electrons being minority carriers into the surface of the substrate can be regulated, resulting in prevention of the loss of carriers.
For example, Patent Document 1 discloses, as a method for manufacturing a solar cell, a method in which a misting method is employed as a method for forming the aluminum oxide film being the passivation film on the p-type silicon substrate. The manufacturing method achieves the effect of forming a passivation film, without inflicting damage to a silicon substrate, with a high degree of production efficiency at lower manufacturing cost by forming the passivation film by the misting method.